Glossary

AU

Astronomical Unit: The mean distance between the Earth and Sun, equal to about 150 million kilometers (or about 93 million miles).

Asteroid

An asteroid is an icy dirtball that orbits the Sun, typically on a almost-circular orbit. Asteroids were once thought to be solid chunks of rock but in the past few decades scientists have realized that most of them are probably "rubble piles" of rock held together by their weak gravitational attraction and mixed with ice. Asteroids are generally more rocky than icy.

Bolide

A bolide is a very bright meteor also known as a fireball. They are considered bright if they are brighter than the brightest planet, Venus. Typically caused by a chunk of rock entering the Earth's atmosphere traveling at about 30 km/s (67,000 mph) and quickly burning up at an altitude of about 100 km (60 miles).

C-type

C-type asteroids are classified into different types by their spectra - the colors of their surface. C-type asteroids have a grayish color. The color is thought to indicate that their surfaces are composed of carbonaceous material resembling soot from a fire.

CCD

Charge Coupled Device: This is the light sensitive "film" in modern digital cameras - from a small point-and-shoot, to the fine digital SLR cameras, to the powerful cameras for the ATLAS system. Llight is captured on little electronic "pixels" that can be directly read and displayed on a computer screen. For detailed information see Wikipedia's CCD page.

Comet

A comet is a dirty iceball that orbits the Sun. Comets were once thought of as solid chunks of ice but in the past few decades scientists realized that most of them are probably "rocky snowballs" held together by their weak gravitational attraction. Comets are generally
more icy than rocky.

Fireball

A fireball is a very bright meteor also known as a bolide. They are considered bright if they are brighter than the brightest planet, Venus. Typically caused by a chunk of rock entering the Earth's atmosphere traveling at about 30 km/s (67,000 mph) and quickly burning up at an altitude of about 100 km (60 miles) due to friction with the Earth's atmosphere.

M-type

M-type asteroids are classified into different types by their spectra - the colors of their surface. M-type asteroids have colors that indicate that much of their surface is covered by metals like iron and nickel.

Meteor

Often known by the term "falling star," like this website. A meteor is the quick and bright flash of light in the night sky produced when a small piece of rock enters the Earth's atmosphere traveling at about 30 km/s (67,000 mph) and burns up at an altitude of about 100 km (60 miles) due to friction with the Earth's atmosphere. A bright meteor might be caused by a pea-size piece of rock. Most the ones we see are the size of grains of sand. Most meteors burn up entirely in the atmosphere creating a fine dust that settles down to the ground.

Meteorite

If a large meteor (a bolide) fails to burn up in its passage through the atmosphere, a part of it might strike the Earth. The remnant that survives on the Earth's surface is called a meteorite.

Meteoroid

A meteoroid is the chunk of rock in space before it strikes the Earth's atmosphere. Meteoroids are asteroids that will strike the Earth's
atmosphere.

NEO

Near Earth Object: An asteroid or comet that approaches to within 1.3 AU (121 million miles) of the Sun.

Orbit

An orbit is the path of an object around another object. The moon "orbits" the Earth and, in turn, the Earth "orbits" the Sun. Orbits are typically elliptical, i.e. egg-shaped or oval.

PHO

Potentially Hazardous Object: An asteroid or comet that is larger than 150 meters in diameter (about 500 feet), which can approach to within 0.05 astronomical units (AU) of the Earth's orbit. This does not mean that it approaches the Earth to within this distance - just the Earth's orbit. These objects are considered hazardous because they are large enough to cause widespread damage on impact and because even though they do not approach Earth closely now, their orbits can change over about 100 years to make them Earth-impacting objects. They therefore
warrant attention.

S-type

S-type asteroids are classified into different types by their spectra - the colors of their surface. S-type asteroids have a reddish color. The color is thought to indicate that their surfaces are composed of silicate material resembling beach sand.